Increased storage capacity in digital disc recording technology has traditionally been addressed through improvements in the ability to store information on a particular storage disc with an increased areal density, e.g., by decreasing a size of the inductive write element and read back sensor in a magnetic recording system. Until recently, these prior art approaches have been adequate for increasing the storage capacity of magnetic recording discs. However, since a superparamagnetic effect limits the theoretical storage capacity of magnetic recording discs, other digital disc recording technologies (e.g., ferroelectric recording technology) are possible alternatives.
Typically in magnetic recording, magnetic vectors of ferromagnetic domains in a storage medium are arranged in a coherent manner to store bits of data. For example, if a vector direction between adjacent domains in reversed, a binary “1” can be stored. However, as the size of ferromagnetic domains in the storage medium are reduced in order to achieve higher packing densities, the anisotropic energy of the magnetic domains decreases. When the anisotropic energy of the ferromagnetic domains falls below what is known as the “superparamagnetic” limit, ambient thermal energy can overcome the magnetic anisotropy of the ferromagnetic domains and cause the magnetic domains to randomly reverse polarity. Therefore, it is not possible to store data on ferromagnetic domains below the “superparamagnetic” limit.
Ferroelectric materials (e.g. ferroelectric thin films) also have spatially localized domains representing individual bits of recorded data. However, with ferroelectric materials, the domains are formed by charged regions rather than magnetic vectors. More specifically, binary data in the form of polarization states can be stored in ferroelectric materials by utilizing one or more electrically conducting write tips as moveable top electrodes to store the data in the domains on the ferroelectric material. The polarization is preserved without the continued application of an external electric field. Since the “superparamagnetic” limit does not apply to ferroelectric recording, ferroelectric domains can be formed much smaller than magnetic domains and thus ferroelectric materials are capable of yielding much higher storage densities than comparable magnetic storage mediums.
A typical voltage pattern for writing bits into ferroelectric media may be characterized as a square wave, with alternating periods of positive voltage and negative voltage with magnitudes at least sufficient to induce polarization switching in the ferroelectric media. However, this voltage pattern suffers from cross-track blooming and along-track blooming problems on the ferroelectric media. As a result, it can be a challenge to maintain the size and location of small ferroelectric domains along a track of the ferroelectric media.